This proposal addresses the role of message characteristics (case history, base-rate information, abstract principles) in the presentation of medical, political, and social messages and the relationship of these characteristics to the persuasion process. We hypothesize that accounts of medical, political and social issues and events draw differentially on cognitive heuristics and that, accordingly, such communications are differentially persuasive (Tversky & Kahneman, 1974). We hypothesize, other things being equal, that case history (colorful, personal, anecdotal) information is more highly available and more persuasive than base-rate or representativeness information (information that relates an incident or person to general class membership) which is in turn more persuasive than abstract principles (anchoring and adjustment information that sets an issue into a social, political or moral context). The research will also examine specific predictions regarding the differential persuasiveness of heuristics as a function of: the contents of the particular issue; the education of the receiver and the type of issue (symbolic versus non-symbolic); and the nature of the case information itself (e.g., causally constructed). The proposed research investigates these hypotheses in the context of current medical, political and social issues, including preventive health behavior, tax reform, abortion, and affirmative action legislation with the goal of developing applied attitude change techniques.